As shown in FIG. 6, in a hitherto ultrasonic flow rate measurement device of this type, an oscillation circuit 3 performs oscillation for a given period of time with an operating frequency set by frequency control means 4 in accordance with a start signal from a control block 6, thereby activating a first ultrasonic probe 2. Ultrasonic waves emitted from the first ultrasonic probe 2 propagate through a fluid to be measured with which a measurement flow path 1 is filled, and a second ultrasonic probe 7 detects the ultrasonic waves after elapse of a time “t.” A comparator 9 compares a thus-detected received signal with a reference voltage 8. When a voltage relationship between the reference voltage 8 and the receive signal has become inverted, a stop signal is sent to a timer 5, to thus deactivate the timer 5.
A thermistor 10 for sensing a temperature is disposed in the measurement flow path 1, thereby measuring a temperature of the fluid to be measured.